Apparatus for uniformly plating a continuous cylindrical substrate

ABSTRACT

Apparatus for electroplating copper onto a wire substrate at very high speeds and continuously, and associated copper electrolytes and plating methods. An essentially hollow cylinder is provided as a plating cell through which the wire can be advanced and along which recirculated electrolytes can be passed. Recirculation inlets are provided to communicate with the central passage and are arranged to ionize the fluid uniformly and inject it into the passage so as to be distributed uniformly about the passing wire and to be directed symmetrically and radially against the wire and then diverted symmetrically and with agitation along the wire toward an exit port. Novel associated electroplating methods and electrolytes, such as copper cyanide and copper sulfate, are also described. The result is to plate copper very quickly, yet uniformly, onto the wire to provide a substrate of controlled surface configuration for subsequent plating of thin magnetic films.

United States Patent Semienko et al.

[ 1 June 13, 1972 [72] Inventors: Peter P. Semlenko, Roslindale; Emil Toledo, Brighton, both of Mass.

[73] Assignee: Honeywell, Inc., Minneapolis, Minn, [22] Filed: Jan. 22, 1970 [2]] Appl. No.: 10,689

Related U.S. Application Data [62] Division of Ser. No. 5l8,l84, Jan, 3, 1966, Pat. No.

HOLES FOR H2 ESCAPE us) COPPER i ANODE 2 T;

F OREXGN PATENTS OR APPLICATIONS l 290,184 2/1960 France ..204/206 Primary Examiner-John H. Mack Assistant Examiner-W. l. Solomon AltomeyCharles J Ungemach, Ronald T. Reiling and James A. Phillips [57] ABSTRACT Apparatus for electroplating copper onto a wire substrate at very high speeds and continuously, and associated copper electrolytes and plating methods. An essentially hollow cylinder is provided as a plating cell through which the wire can be advanced and along which recirculated electrolytes can be passed, Recirculation inlets are provided to communicate with the central passage and are arranged to ionize the fluid uniformly and inject it into the passage so as to be distributed uniformly about the passing wire and to be directed symmetrically and radially against the wire and then diverted symmetrically and with agitation along the wire toward an exit port. Novel associated electroplating methods and electrolytes, such as copper cyanide and copper sulfate, are also described. The result is to plate copper very quickly, yet uniformly, onto the wire to provide a substrate of controlled surface configuration for subsequent plating of thin magnetic films.

3 Claims, 2 Drawing Figures COPPER ANODE CONNECTOR FOR SOLUTlON SUPPLY TEFLON INSERT (Tl WlTH HOLE(B) COPPER 2i ANODE PKTENTEU N I97? 3,669,865

TEFLON INSERT (7) WITH HOLE (8) H lwm HOLES FOR n ESCAPE PETER P. ssmsmro EMIL rousoo mvmwon BYMjMJ- A TTORNE Y APPARATUS FOR UNIFORMLY PLATING A CONTINUOUS CYLINDRICAL SUBSTRATE This application is a division of application Ser. No. 518,184, filed Jan. 3, i966 and now U.S. Pat. No. 3,506,546.

The present invention relates to a novel plating arrangement for electroplating metal to a cylindrical substrate and to methods therefor; more particularly it relates to a plating arrangement providing means including fluid dispersing means and associated charging means for more uniformly distributing plating electrolyte, and charged ions therein, adjacent such a substrate and thereby improving the speed and uniformity of plating.

Control over the uniformity of plating is often important to workers in this art. it is critically important, however, to workers engaged in the plating of substrate surfaces for the subsequent deposition thereon of thin magnetic films, since departures from a prescribed uniform plating rate can radically change the magnetic properties of such a film; for instance, by varying the crystalline structure of the plated substrate, introducing stresses therein, changing the grain size thereof and the like. Any one of such changes can be fatal to deriving a prescribed magnetic property, such as minimal magnetostriction. Thus, it is an object of the invention to provide a technique and associated means for improving the uniformity of plating a metallic layer onto cylindrical substrates, even while the substrates comprise continually moving filaments, such as copper alloy wire. An associated object is to provide means for dispersing the plating electrolyte in a prescribed manner and distributing it symmetrically inward, radially, against such substrates moving through a plating cell. A related object is to provide means for creating a homogeneous distribution of charged ions in such electrolyte. Still another object is to provide a novel electrolyte and associated plating conditions apt for employment with such distribution means, especially under high current density, fast plating operating conditions.

It will be evident to those skilled in the art that non-uniform plating can also degrade a plated film by introducing roughness and surface discontinuities therein. it is axiomatic in the plating art that roughness is a relatively irreversible process, that is, as a plating deposit proceeds to build up, it can never be smoother than either the substrate it initially encounters or that created during build-up. Thus, in electroplat ing copper onto a moving filament, any discontinuity in the plating rate along the length of the plating cell will create roughness discontinuities which thereafter will further build up at the same or greater roughness. Hence, for such a case, workers in the art appreciate that for smooth plating it is important to maintain a uniform plating rate along the active length of a plating cell while a substrate is moving therethrough. The present invention provides a novel cell structure and novel electrolyte apt for producing such uniform plating and additionally provides a unique control over plated roughness. Workers in the art will acknowledge that controlling plated roughness is something much desired and long awaited in the art of plating a substrate for deposition of thin magnetic films.

IN GENERAL The invention is intended to provide improved faster electroplating of copper on a moving filamentary substrate to relatively thick layers with good control over surface homogeneity and smoothness. Such a substrate may comprise any metal wire, such as beryllium copper drawn wire or the like. This substrate should have a reasonably smooth surface within the limits expected on the plated copper film.

According to the invention a standard drawn wire may be advanced continually through the novel electroplating cell in; cluding a plurality of recirculation fluid inlets disposed relatively unifonnly along the length thereof, each inlet having an ionizing means associated therewith. A plurality of fluid-diversion means are provided within the cell to coaxially surround the wire, each communicating with an associated one of the inlets to divert the fluid therefrom in a prescribed helical dispersion mode for impelling the charged electrolyte against wire substrate to pass contactingly therealong, thus maintaining the composition of electrolyte adjacent the filament uniform and undepleted. The fluid-diversion means are preferably perforated to allow escape of hydrogen bubbles from adjacent the wire. A particular embodiment of such a cell structure is indicated in FIGS. 1 and 2 and described below.

A preferred copper plating electrolyte has been developed for use with the above cell, such as will be operable at the typical, extremely high current densities for providing fast, highly efficient plating rates, yet with unifonnity and smoothness. Such an electrolyte comprises a Copper Cyanide bath, such as is indicated in Table l operated at prescribed ranges of bath temperature, Cyanide and Copper concentrations.

A particular embodiment of the invention including a prescribed plating electrolyte and associated plating method will now be described with reference to a particular filamentary substrate, namely a beryllium-copper wire of about 5 to 8 mils diameter and of a prescribed unifonn shape, smoothness and freedom from discontinuities. For instance, such a wire may be immersed in an acid electro-lyte to be electrolytically drawn or reduced to a prescribed uniform diameter and smoothness, for instance, as described in a co-pending commonly assigned application to P. Semienko and E. Toledo entitled Metal Treatment Ser. No. 5 I 8,013, filed Jan. 3, 1966, and now U.S. Pat. No. 3,556,957. The wire being thus normallud in diameter and surface finish with a uniform smoothness and absence of discontlnulties Is continually advanced through a following series of treatment stations, such as by drawlng the wire from a spool continuously at about 5 inches per minute. The wire may first be advanced through a clean water rinse and thence to a cathodic neutralization station. The neutralization is provided, first to neutralize any acidic residues on the wire and second, to clean the wire surface for subsequent copper plating. The neutralization bath thus comprises a basic aqueous cleaner which will not attach the (copper alloy) wire and preferably includes an aqueous mixture in the proportions of: 23 grams sodium carbonate, 23 grams sodium phosphite tribasic and 46 grams sodium metasilicate in about one liter of water, or similar proportions. This bath is kept at room temperature and includes a cylindrical Lead anode for producing a relatively uniform cleaning current ofabout 20 Ma/Cm as known in the art.

PLATING CONDITIONS After cleaning, the wire is advanced through a clean water rinse and thence through a copper electroplating station. A very substantial layer of copper is deposited very quickly and very smoothly according to the invention, both to improve the "plate-ability" of the metal filament substrate and to improve the magnetic characteristics thereof. Typically, this thick copper layer may be as thick as about one-half mil or more.

The technique of rebuilding a wire substrate by depositing a substantial layer of copper thereon may be implemented in various ways, using a novel electrolyte and associated plating parameters, together with a new cell structure as will be described herewith. A number of copper plating baths were investigated, but the most satisfactory was an aqueous cyanide bath comprising the following constituents, indicated in the Examples of Table I.

These examples are intended to more fully illustrate the invention which should not be limited to the specific substrates, electrolytes, and plating conditions described, but rather include all equivalents evident to those skilled in the art and within the scope of the invention as claimed.

TABLE I Ex. I

(preferred) 60 g.(to proper Cu Conc.)

90 g.(to adjust free cyanide cone. to: 17 (1- 2) gJL.) 30 g.

Copper Cyanide Sodium Cyanide and/or Potassium Cyanide 5-40 (pref. 15-25) 8-/L, Sodium Carbonate Vary 25% (pref) Sodium Hydroxide 20 g.(rnin. l g./L.)

mode transport Double Anodes, lnlets and Diverters From about 1 micron at 50 Ma/Crn to about 6 microns at 400 Ma/Cm Cell structure Typical plating thicknesses (about 1.3 min. total immersion time) Max. smooth plated thickness Over 11 microns Table 1 indicates preferred conditions for plating the above copper coating and, employing the indicated ingredients at the indicated conditions, preferably uses a plating cell about eight inches long including highly active agitation means and associated ionizing means and the like for assuring homogeneous charge density and bath composition throughout, especially adjacent the wire. The free Cyanide concentration should be kept near the indicated level since an increase tends to degrade plating efficiency, though it improves smoothness. Large increases can even be noxious. For example, a concentration of about 10 grams derived a much rougher coating than the indicated 17 gram concentration, while 40 grams was too inefficient to plate a sufficiently thick layer. (Efficiency is proportional to plated thickness per minute at a certain current density.)

A feature of the invention is that smoothness may be controlled for constant plated thickness by simply adjusting Cyanide concentration and, compensatorily, current density, Thus one may increase Cyanide concentration to get a smoother coating and since this also tends to reduce plated thickness, may increase current density sufficient to compensate. Either sodium cyanide, potassium cyanide, or a combination, may be used as a source of cyanide. As to the concentration of copper, concentrations substantially lower than that indicated (for instance, 26 grams per liter), produced a dull, largegrained finish whereas concentrations substantially higher (for example at 58 grams per liter) yielded a very rough surface. The range of specific gravity provides a handy check as to proper concentration of copper. As to bath temperature, below the indicated range (for instance, at 30), a rough grain was derived; whereas substantially above it (such as at 80 C. the bath tended to become unstable and presented a health hazard because of the likely evolution of Cyanide fumes. Various equivalent baths, both acidic and basic, will occur to those skilled in the art; however, the following were found somewhat less satisfactory, namely baths consisting esscn tially: of copper sulfate; of Rochelle Cyanide; of Pyro phosphate; and of common commercial copper leveling solu- "OHS.

Using the copper plating cell indicated in FIG. 1 and under the plating conditions summarized in Example l, it is possible to plate at uniquely high current densities, as high as about L250 amps/ft (600 Ma/Cm) plating at about 3 microns per minute with high (magnetic-plating") smoothness (that is, to plate about 10 microns diameter thickness on wire W, moving at in/min. through the 8 inch cell of FIG. 1). By contrast, workers have been heretofore been limited to a maximum of about 50 amps/ft and about one-half micron per minute for smooth copper plating apt for a magnetic film substrate. The latter rate is so slow that it has made it impractical to plate more than about one micron or wires which are conventionally advanced at about 5 inches per minute, since it is impractical to use plating cells longer than about ten inches. Further, the plated surface smoothness, has not been reliably controllable even at this slow rate, unlike with the invention. It will be recognized that the novel electrolyte and the novel cell design according to the invention, creating a high helical agitation and an even current distribution, have derived this radical improvement in copper plating.

Workers in the art will recognize that this precise control over roughness is critical for certain applications, such as providing a substrate for magnetic plating, and that it has been heretofore unavailable. it is surprising that the described electrolyte and plating cell have been able to achieve the indicated improvements in both smoothness control and plating efficiency. Current densities as a function of the approximate thickness of plated copper are indicated in Table II along with the smoothness derived. It is assumed that the bath conditions in Example I obtain with an approximate 1-56 min. immersion time.

TABLE [1 Variation of Plated Thickness With Current Density in Example I Plated Thickness Variations CD (Ma/Cm) (microns radially) (:l: microns) Finish 2 0.] .05 Very smooth 8 0.4 .10 Good 18 0.9 .20 24 1.2 .20 36 1.4 .20 48 1.8 .20 Fair 200 3.5 .50 Fair 600 5.0 10 Poor PLATING CELL FIGS. 1 and 2 indicate sectional side and end views, respectively, of an embodiment of a novel plating cell arrangement according to the invention for plating copper, or any material, to a substrate with improved uniformity and efficiency. A copper plating cell 1 is mounted in a tank T adapted to be filled with the intended copper plating solution (such as that of Example 1 above). It will be understood that a plurality of such plating units (like cell 1 in Tank T) may be required where larger amounts of copper must be plated on the moving substrate (wire W), being preferred to a single long cell for reasons of geometry and the like. However, under the conditions indicated above, the use of one such cell about 8 inches long (about 7 in. active length; 1.3 min. immersion time at Sinch/min. speed) was sufficient to plate several microns of copper very quickly, yet with controlled smoothness under the conditions of Example I. Tank T includes a recirculating line of a type known in the art and comprising a recirculating pump P and associated conduits for removing the plating solution from the bottom of Tank T at a prescribed rate and injecting it into an elevated reservoir (not shown) from which it may be gravity-retumed to plating cell 1, as needed, through two or more similar reinjection/ionizing means spaced relatively equidistant along cell, such as top conduits 21, 21' and associated ionizing anodes 25, 25. The cross-sectional areas of conduits 21, 21' (diameters 23, 23') should be similar to provide a uniform rate of fluid injection longitudinally along cell 1. These injection apertures together with the elevation level of the reservoir etc. will of course determine the rate at which plating fluid is re-circulated to cell 1. For the indicated arrangement, a pair of tubular conduits 2|, 21', each having an inner diameter 23, 23 of about three-eighths inch was found adequate.

Plating cell I generally comprises a cylindrical tubular body 3 of Plexiglass with conduits 21, 21' arrayed relatively equidistant along the top length thereof. It was found satisfactory in the indicated arrangement to employ a tube 3 about 7 inches long with an inner diameter of about 3/4 inch. The ends of tube 3 are capped by a pair of Plexiglass disc caps 5, 5', each having a bore centrally thereof which is adapted to receive a Teflon insert 7, 7', themselves, each have a like central bore 8, 8, respectively, which is of sufficient diameter (eg 50 mils) to allow Wire W (about 5 to 7 mils diameter) to be advanced continually therethrough, as indicated by the arrow, leaving a prescribed clearance radially therearound. This clearance should be large enough to allow the escape of a prescribed amount of plating solution, but sufficiently small to keep the plating fluid at or near the top of the inside of tube 1. Secured within the bore of cylinder 3 are a pair of Plexiglass agitation-directing units, or shields, 11, 11' comprising similar relatively cylindrical, hollow tubular bodies l4, 14' each having a solid flange portion 18, 18' extending outward at one end thereof to engage Tube 3. Tubes 14, 14' also have central concentric bores l9, 19' respectively adapted to conduct plating fluid along wire W opposingly and a plurality of radially-extending flange-sectors l7 and 17', respectively. As best indicated in FIG. 2, Sectors 17, 17' are disposed relatively symmetrically about the circumference of tubes 14, 14', respectively, at one end thereof to engage the inside of cylinder 3 for positioning engagement therewith as with solid flanges l8, 18' at the opposite ends of tubes l4, l4. Sectors l7 and 17' are spaced circumferentially from one another by fluid-conducting apertures and 15, respectively, which are arranged, according to a feature of the invention to introduce the fluid from associated conduits (21, 21) into cell I adjacent Wire W in a prescribed helical agitation mode. It has been found that locating three or more apertures l5, l5 relatively symmetrically about the circumference of tube 3 can impart a very desirable helical agitation of the introduced plating fluid about Wire W, both in the intershield area L of cell 1 and therebeyond, along Wire W, through bores l9, l9 and toward the outlets adjacent inserts 7 and 7' respectively. The total crosssectional area of apertures 15 and apertures 15' must be similar and be as large as (preferably somewhat larger than) that of the associated conduits 21, 21' respectively. Thus, sectors l7, 17' will have a prescribed radial size sufficient to engage the inside of tube 3 and a prescribed circumferential width sufficient to leave apertures l5, 15 of the prescribed cross-sectional area. The cross-sectional area of bores 19, 19' through tubes l4, 14, respectively, is related to that of any of their associated supply passageways, namely passageways 21, 15 and 21', 15', respectively, being substantially smaller to increase the velocity of the fluid therealong, It was found that an area for bores l9, 19' of about one-third to one-quarter that of conduits 21, 2] gave satisfactory speed and agitation with the described arrangement.

Typical paths for the fluid through this helical agitation arrangement of shields 11, 11 are indicated by the arrows A, B, C and A, B' C, respectively. For instance, arrow A indicates the entry of injected fluid from conduit 21, its subsequent distribution through apertures 15; and then its injection, in a helically agitating manner, into the inter-shield region L to be there rolled around. The fluid then is turned to enter bore 19, as arrow 13 indicates, following Wire W therethrough in a helical screwlike motion to emerge therefrom and, passing on, (per arrow C) to exit through bore 8 in insert 7. (Similar with arrows A, B, C' for shield l 1'). It will be understood by those skilled in the art that this form of agitation and equivalent forms may be provided by additions to. substitutes for and modifications of the indicated structure. For instance, it may be advantageous to add turbine-like deflector vanes along the exterior of tubes l4, 14' to direct fluid shearingly and more efticiently through apertures l5, 15'. It will be appreciated by those skilled in the art that the continuous and well-determined agitation of the plating fluid provided by shields ll, 11 as indicated above, will assist in keeping the bath composition homogeneous throughout cell 1 (along Wire W) and hence maintain the rate of copper deposition relatively uniform along the length of Wire W within cell 1 especially along portions thereof within the shields and therebetween.

More particularly, it will be appreciated that this agitation being made helical or the like and thereby given components of motion in both the horizontal and vertical directions (arrows H, V, respectively), it will prevent the customary depletion layer from forming circumferentially about Wire W. Workers in the art will appreciate the advantages of such an agitation arrangement for destroying this depletion layer and preventing it from interfering (as it commonly will) with the replenishment of plating fluid of the prescribed composition adjacent Wire W. In efi'ect, such agitation provides a homogeneous source-ion concentration adjacent Wire W along its entire length and thus provides a uniform rate of deposition therealong. It will be recognized that a uniform deposition rate along Wire W is critically important since nonuniforrnities can cause harmful discontinuities in deposited crystalline structure. Such agitation also prevents depletion from degrading plating efficiency, since the plating rate should desirably be a uniform maximum along the entire length of cell 1.

According to another feature of the invention, shields ll, 11' are provided with a plurality of radially-bored vent holes 13, 13' and 16, 16' distributed somewhat evenly along the length of the tubular portions l4, 14 thereof. The longitudinal distribution of holes l3, 16 will be appreciated from FIG. 1; whereas the circumferential distribution is best indicated in FIG. 2, the pair of upper holes being characterized as 13' and the lower holes as 16. It will be appreciated that the exact number and location of these holes is variable within the contemplation of the inventionv The purpose of holes 13, 16 etcv is to allow the escape of hydrogen gas bubbles from around Wire W in the region of bores 19, 19', upwardly, through tubes 14, M. Thus, the number (density) of holes longitudinally along tubes l4, 14' should just be enough to dissipate substantially all the likely bubbles, while the number (density) circumferentially should be sufficient to assure that at least one row thereof will be positioned relatively above Wire W no matter how the shield 11, ll is fixed in tube 3, thus allowing random shield-orientation conveniently. It will be appreciated that such bubble dissipation removes a common cause of dropouts," and other plating discontinuities, along Wire W, since an agglomeration of such hydrogen bubbles can position itself adjacent Wire W and shield the wire substrate from proper deposition of copper.

According to another feature of the invention, plating cell 1 also includes a pair of ionizing copper anodes 25, 25', one being provided adjacent each conduit (21, 2t, respectively) being introduced therethrough and arranged to advantageously provide a highly uniform distribution of charged ions in the injected plating fluid and thus along the length of Wire W within cell 1. It will be recognized that the function of anodes 25, 25' is to ionizingly charge ionic particles in the plating fluid being introduced therepast, these particles being transported to the vicinity of Wire W by the circulating fluid to thus establish a plating current between the anodes and Wire W. Anodes 25 will be constructed to comprise conventional plating electrodes known to the art, being preferably made of highly conductive copper, shaped relatively rectangularly and spaced not so far from Wire W as to introduce any appreciable resistance losses therebetween. The mass of the anode should of course be sufficient to provide long life since it will be somewhat dissolved by the plating. Anodes 25 may alternatively be positioned anywhere enabling them to so intercept injected plating fluid as to maintain a relatively uniform charge density along Wire W (especially in regions L, l9, l9 The position of the anodes will provide this uniformity, preferably providing one anode to charge the fluid emerging from each injection point (21, etc.) as shown, or the equivalent. This position is not directly related to the location of Wire W since, in the described dynamic plating, no field effects are involved (unlike static capacitive" plating).

Anodes 25, 25' are charged at a suitable positive DC potential relative to Wire W, preferably each being charged at the same potential. For example, anodes 25, 25' have been charged from a plus 15 volt DC source which was regulated to rangement of anodes for providing a uniform distribution of charged ions adjacent Wire W, improves the uniformity of the plating rate along W, thus improving the smoothness and crystalline homogeneity of the plated copper deposit. As will be understood by those skilled in the art, such an arrangement also permits operation with very high plating current densities and thus higher plating rates and much greater plating thicknesses than heretofore known in the art.

The above copper plating features are unique in the art; for instance, providing a higher plating efficiency for coating magnetic substrates smoothly than known heretofore and providing much closer control over the roughness and crystallinity of a plated copper coating. Roughness control is vitally important for allowing plating of satisfactory thin magnetic films, which may, for instance, require a (substrate) roughness of between about No. 2 and No. 8 (STM), no more and no less. The invention can uniquely control roughness per se, keeping other characteristics constant by simply increasing Cyanide concentration to improve smoothness, while raising current density correspondingly to compensate for reduced thickness. Such roughness control can greatly simplify any subsequent polishing steps such as those below, at times making polishing possible where before it was impossible.

The invention will be thus recognized as providing an improved structure and method for plating a substantial thickness of copper to a beryllium copper wire substrate subsequent to providing a relatively smooth, homogeneous wire surface therefor, especially for producing improved wire substrates for plating thin magnetic films. While the novel copper plating can provide control over roughness of the plated copper, a finer control will at times be employed supplementarily.

ELECTRO-POLISHING Subsequent to the drawing and copper coating treatments above, it is preferred to electro-polish the coated (rebuilt) filament, also continuously, since the coating may not be smooth enough for certain applications, such as depositing thin magnetic films. it is especially preferred to electro-polish with a novel sulfamic acid bath, particularly when the filament is to be used as a substrate in sulfamate type magnetic plating solutions. The current density will be varied according to the amount of polishing desired.

The copper-plated wire is therefore next continually advanced past the coppering station through a clean water rinse and beyond to an electro-polishing station, where the copper finish may be finally smoothed and also be sensitized for subsequent magnetic plating. The electro-polish is performed by a smoothing electrolysis using an aqueous Phosphoric acid Sulfamic acid bath, such as indicated in Examples II, III or IV below. A sulfamic electro-polish bath is provided according to the invention to polish both smoothly and efiiciently, while also reducing contamination of the substrate and dropouts during subsequent plating. For instance, eliminating the sulfamic acid constituent from a phosphoric acid bath has been found to induce the formation of oxidation sites (blocking subsequent plating). Similarly, using sulfuric acid alone corrodes the copper layer catastrophically, leaving intolerable discontinuities therein. The sulfamic type baths act to reduce the activity of the polishing bath and inhibit post-copper-plating oxidation (which degrades subsequent magnetic plating), thus providing the best control over "plateable" surface finishing at a minimum loss of plated copper thickness. For instance, they can produce a reproducible surface-leveling of from 1 to 300 micro-inch RMS for "dropout" free magnetic plating. The preferred electro-polishing conditions are indicated for Examples ll, III, IV below, wherein it will be presumed that the above-mentioned on-line wire treating conditions apply, such as advancing the wire at 5- inches per minute and wherein the cell used is understood to include a cylindrical bead polishing cathode as known in the art.

$0 gJL, water) Bath at room temperature Current density-time immersed 2-50 Ma/Cm' (Pref. II) for 50 sec.

Sulfamic acid may be used up to the solubility limit of concentration to maintain smoothness, but about 20 gm. sulfamic acid per liter water is preferred.

The above polishing steps have achieved a surprising smoothness when used with the copper plated wire aforementioned, reducing roughness a predetermined controlled amount for instance from No. 40 (STM smoothness: microinches, peak-to-peak) to as little as No. l. Any desired smoothness on the order of up to 3 percent of a typical plated thickness (about one micron i.e., l0 micro-inches) has been achieved. For instance, with Example IV above, a current density of 50 Ma/Cm will level a 4 micron copper coating on 5 to 8 mil wire to about No. 4 STM roughness, reducing wire thickness only about 1 micron.

The acid concentration and other polishing conditions may be varied as understood by those skilled in the art. This electro-polishing step may also be applied to other metal (coatings) substrates from the copper family, such as copper alloys, silver alloys, etc. It is not applicable for such metals as nickel, iron or their alloys, however.

The formed, copper-plated, electro-polished wire is now ready for use and, for instance may be continually advanced further, through a following clean water rinse and thence to a magnetic plating station for providing a thin magnetic film ofa few microns, such as by electroplating a nickel-iron magnetic film from a sulphamate type solution.

It will be apparent to those skilled in the art that the principles of the present invention may be applied to different embodiments from that shown; for instance, to other types of metal plating on other types of substrates, filament and otherwise, for improving smoothness and efficiency of plating and especially for smoothly plating relatively thick layers of copper efficiently, yet to a "magnetic-plating" smoothness and homogenity. The novel plating cell may be used with other electrolytes for plating copper or any metal with improved efficiency and uniformity. Likewise, the electropolishing step may be used to subsequently smooth such copper type coatings. While in accordance with the provisions of the statutes, there has been illustrated and described the best form of the invention known, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus and material and the steps of the method here disclosed without departing from the spirit of the invention as set forth in the appended claims and that, in some cases, certain features of the invention may be used to advantage without a corresponding use of other features.

Having now described the invention, what is claimed as new and for which it is desired to secure Letters Patent is:

1. Apparatus for uniformly electroplating a moving cylindrical substrate, comprising:

bath container means adapted to accommodate said substrate; plating cell means disposed in said container means and including an entry, and an exit aperture through which said substrate may be advanced, a pair of outlet means adjacent each of said apertures and adapted to pass electrolyte therethrough at a prescribed rate into said container means, a plurality of fluid inlet means equispaced along said cell means and adapted to introduce electrolyte into said cell means to approach said substrate at a prescribed uniform rate along said length, a plurality of fluid-diversion means disposed internally of said cell means in fluid-communicating relation with one of said inlet means, each fluid-diversion means including a hollow cylindrical tube having a prescribed internal bore longitudinally therealong and a radially extending flange portion extending radially outward from one end thereofinto engagement with said cell means and also including a plurality of like radially-extending diverting vanes disposed symmetrically about the other end thereof to engage said cell means, said vanes being circumferentially separated by like passageways of prescribed cross-section, said cross-sections totalling considerably more than the crosssection of said bore; a plurality of charging means, one charging means associated with each of said inlet means and arranged to uniformly ionize the electrolyte fluid passing therethrough in a prescribed manner; and recirculation means arranged between said bath container means and said inlet means so as to transfer electrolyte therebetween.

2. The combination as recited in claim 1 wherein said plurality of inlet means and associated fluid diversion means comprise a pair thereof, said fluid diversion means being disposed opposingly to divert fluid in a helical mode toward one another and thence re-entrantly along said associated bore toward an associated one of said outlet means, said outlet means comprising an oversized one of said entry and exit apertures, respectively.

3. The combination as recited in claim 1 wherein each of said tubes includes a plurality of similar sets of like holes extending radially outward from said bore, being adapted only to allow the egress of hydrogen bubbles therefrom; said hole sets being spaced relatively uniformly at prescribed locations along the length of said associated tube and each comprising a plurality of said holes disposed relatively symmetrically around the circumference of said associated tube at each of said locations therealong 

2. The combination as recited in claim 1 wherein said plurality of inlet means and associated fluid diversion means comprise a pair thereof, said fluid diversion means being disposed opposingly to divert fluid in a helical mode toward one another and thence re-entrantly along said associated bore toward an associated one of said outlet means, said outlet means comprising an oversized one of said entry and exit apertures, respectively.
 3. The combination as recited in claim 1 wherein each of said tubes includes a plurality of similar sets of like holes extending radially outward from said bore, being adapted only to allow the egress of hydrogen bubbles therefrom; said hole sets being spaced relatively uniformly at prescribed locations along the length of said associated tube and each comprising a plurality of said holes disposed relatively symmetrically around the circumference of said associated tube at each of said locations therealong. 